The present disclosure relates generally to aircraft and, in particular, to a method and apparatus for controlling an aircraft. Still more particularly, the present disclosure relates to a method, apparatus, and computer program product for controlling actuators in an aircraft.
A flight control system in an aircraft may include flight control surfaces, controls in a cockpit, connecting linkages, actuators, and other suitable components to move the flight control surfaces. Movement of these flight control surfaces controls the direction of an aircraft in flight. These flight control surfaces may include, for example, a rudder, elevators, flaps, ailerons, slats, spoilers, and other suitable types of control surfaces. The controls in a cockpit that may be used include, for example, a control column and wheel, rudder pedals, a center stick, a side stick, and other suitable controls. A control column may be used to move elevators and/or ailerons. The rudder pedals may be used to move a rudder on a vertical stabilizer and/or spoilers.
Checks of a flight control system may be made at different points in time in the life cycle of an aircraft. For example, a check of a flight control system may be performed while an aircraft is undergoing a certification process prior to delivery. These checks also may be made prior to each flight of an aircraft and/or during maintenance.
One of the operations that may be performed during a flight control system check is to move a control to travel stops for the flight control surface in both directions. A travel stop is any predefined position within a flight control system. This travel stop includes, for example, neutral, detents, and end stroke positions.
For example, the column may be moved to travel stops for the flight control surface in both directions to verify that freedom of movement occurs and that the controls return to the center. Movement of rudder pedals to the travel stops in both directions may be performed to verify the freedom of movement of the rudder and rudder control system, the normal feel force of rudder pedals, and that the rudder pedals return to the center position. During these operations, the operator may confirm that with a full input to a control in the cockpit that the respective flight control surface and the control system both reach full travel in both directions.
For example, with rudder pedals, the rudder control system and rudder travel to their stops with the movement of the rudder pedals to the full travel in both directions. These types of tests may generate loads on the rudder actuation system for the rudder control system and structures associated with the rudder actuation system. Further, with these types of tests, the redundant actuation systems for the rudder are also moved at the same time.
Redundant actuation systems are used to control the aircraft control surface, such that an improperly functioning actuation system does not result in an inability to move that control surface. This type of redundancy may result in a number of different issues. For example, a force fight between actuators may occur when one actuator arrives at a proper commanded position and then the actuator is moved by a second or third actuator, which has not yet reached the proper commanded position. This type of condition results in one actuator opposing the force of another actuator. Further, additional force may occur in the form of a bottoming load when an actuator reaches a travel stop. The loads generated by these checks may be referred to as control check loads.
Performing this type of control check in pre-flight and during maintenance may result in a large percentage of the lifetime fatigue loads placed on these actuation systems. During the certification phase, the control check load on the actuation systems is measured. If the control check load is greater than the load taken into account in the design phase, a redesign may be required before the aircraft can be certified.
Existing parts may be removed and replaced with new parts. This type of process is currently used to prevent undesired loads on the flight control system during actual use. The redesign may include strengthening the actuator, the structures associated with the flight control surface, and other suitable components. The strengthening of these components may include selecting a different material, increasing the amount of material, or other design and/or structural changes.
This type of redesign may increase the life of these components either by increasing the allowable stress by changing material or by insuring the stresses due to control check loads are equal to and/or less than the ones taken into account in the design of the systems. The material change may be, for example, aluminum to steel. This redesign, however, may increase the expense and time needed to certify an aircraft. Weight will be increased in either instance. Further, during the entire life cycle of an aircraft, various components may change in performance in a manner that may increase the control check load above what is desired based on the original design of the aircraft.
As a result, this type of situation currently requires the aircraft to be taken out of service for maintenance in which various structures, such as the actuator and fittings, are replaced with the redesigned components. This type of process increases the expense for maintaining aircraft. Also, this situation may result in the aircraft being out of service for additional periods of time.
Further, in providing new parts and/or redesigned parts, the time needed for suppliers to provide these parts may result in increased time to certification and/or time that an aircraft is out of service.
Modern aircraft actuation control systems employ closed-loop control with the associated electrical hardware and software. The electrical hardware may change with time. Thus, a periodic rigging process may be added to reduce the tolerance effects that may occur. A periodic rigging process includes a manual calibration and/or adjustment of the electrical hardware and software in each actuation system to match the actual position of the control surface. The rigging process also increases the expense for maintaining an aircraft. The rigging takes time, and the aircraft is unavailable when this process is performed.
Therefore, it would be advantageous to have a method and apparatus that may take into account one or more of the issues discussed above, as well as possibly other issues.